Complications arising from reduction of blood supply to the heart are a leading cause of death and debilitation worldwide. Depending on the duration and severity of the ischemic event, irreparable alterations in cellular homeostasis lead to necrotic cell death. However, reperfusion of viable cardiac tissue can result in cell death by processes unrelated to necrosis. This has been attributed, in part, to increases in the production of oxygen radicals and the induction of programmed cell death, termed apoptosis. The proteasome, a major intracellular proteolytic system, appears to play a critical role in the prevention of apoptosis by degrading certain pro-apoptotic factors. Nevertheless, the proteasome is itself modified by free radical processes and exhibits dramatic declines in activity as a result of coronary occlusion/reperfusion. Furthermore, proteasome expression and specific activity decrease as a function of age. The objectives of the proposed research are to establish a mechanistic link between age and free radical induced loss in proteasome function and stimulation of the apoptotic process during coronary occlusion/reperfusion. Utilizing a physiologically relevant in vivo rat model of coronary occlusion and reperfusion this study seeks to: 1) Identify alterations in proteasome activity; 2) Defme free radical processes which result in loss in proteasome activity; 3) Characterize the progression of apoptosis; and 4) Establish mechanisms by which proteasome inactivation enhances apoptosis. In each aim, the effects of duration of occlusion and reperfusion and age of the animal will be assessed. Thus, these studies will establish biochemical mechanisms by which proteasome function is altered and when, in the sequence of coronary occlusion and reperfusion, critical oxidative events occur. Furthermore, the role of proteasome inactivation in the induction of apoptosis will be established. Finally, the contribution of age-dependent declines in proteasome activity to the progression and extent of coronary occlusion/reperfusion induced apoptosis will be elucidated. Results of the proposed study will therefore define molecular events which are likely to impact the long term progression of heart disease and indicate efficient strategies for favorably influencing the outcome.